Ok first it's time for you to learn about the WD sleep mode. Leave the disk un used for a little time, then acces it back, there will be a little delay before the disk will open that you don't have on most of the other drive. This is because the head is going back at the idle position. The samsung is not doing that, making it faster and better for raid when compared to a WD Caviar green.
I also never tell the Caviar black would be cheaper but a good alternative. Since they are faster it's normal the price is higher compare to the Samsung one.
FInally, I spend my whole day fixing computer and the experience told me never to trust those LP drive because they have high rate of failure. They are also, like all seagate drive, doing a lot of noise. Especially the 7200.11.

I've not noticed much difference with the WD green drive and sleep mode. it's a low power and green drive for a flippin' reason anyways. I know of the technology, but at least on the windows side you can disable most of the sleeping functions. not the core stuff, but that sleep mode that matters most. (IMO) REGARDLESS, none of the green or eco drives are good for RAID, but I still think Seagate is the best of the greens.

and you must still hate the deathstars and by that coin, Hitachi then too eh? Seagate has an issue with some of the green drives, the 1.5 TB ones in particular it seems (probably due to the popularity of that size earlier on). the ones I have ironically. But the Caviar Greens (among the others) in particular have their fair share of failures too. It might be less then Seagate but it's still there. I don't see though, how you can recommend pairing a WD black and say it's "perfect and will run like your samsung." .. the black will be vastly more superior then the samsung, also at $40 more per drive. I thought the OP was trying to save the dollars?